1. Field of the Invention
The present invention relates to an image recording apparatus for recording an image on a sheet by jetting an ink from a plurality of nozzles.
2. Description of the Related Art
As an example of an image recording apparatus, an inkjet printer is for recording an image on a recording medium retained and conveyed by a conveyance mechanism in a high speed and high image quality by jetting an ink droplet from a plurality of nozzles of a print head. The inkjet printer is widely used for an office use for recording an image on a recording medium (i.e. a sheet) of a cut sheet form for instance. In recent years, the inkjet printer is also used for an industry use for recording images on a recording medium (i.e., a continuous sheet) such as a roll sheet as a result of a successful improvement of a throughput by constituting a line head arraying a number of print heads in a direction perpendicular to the conveyance direction of the recording medium.
In such an image recording apparatus, one of effective means for conveying a sheet in a cut form and a continuous sheet such as a roll sheet is conveyance means using a drum. In the case of using a drum for a conveyance mechanism, the print head is retained by maintaining a prescribed gap in relation to the drum for recording an image on the recording medium. In order to maintain a print quality, the print head requires maintenance for each prescribed time period. For this, the print head is retracted from the drum for forming a space between the print head and drum by an elevation mechanism when carrying out the maintenance of the print head. The maintenance of the print head is carried out by inserting a maintenance unit into the space. Upon finishing the maintenance of the print head, it is returned to the image recording position for recording an image by the elevation mechanism. In this event, the gap between the print head and drum always needs to be identical before and after the maintenance. That is, unless the print head is retained by keeping a prescribed gap in relation to the drum, an occurrence of a color shift, or such, is caused. As an example, a Laid-Open Japanese Patent Application Publication No. H11-277764 has disclosed an invention for making it possible to maintain the gap between a print head and a drum securely at a prescribed value before and after maintenance by three points holding mechanism.